This invention relates to an electronic musical instrument of digital processing type, and more particularly to an electronic musical instrument in which a glissando effect and a portamento effect can readily be provided by conducting automatic calculations on key codes.
Various types of electronic musical instruments have recently been developed with rapid advance in electronic technique. Electronic organs, typical electronic musical instruments, are widely used because they can produce many types of tone colors and various tone effects thereby enabling versatile rich expressions of music and because they can readily be performed by even not skilled players. The electronic musical instrument of this type forms musical tones by electronic means different from such natural musical instruments as pianos and pipe organs. When classified according to the method of forming musical tones the electronic musical instruments are classified into a tone signal keying system and a synthesizer system. The tone signal keying system is applied to the conventional type electronic organ according to which tone source signals having frequencies corresponding to the tone pitches of various keys are provided, and the tone source signals of the tone pitches of the operated keys are selected by the operation of the keys of a keyboard unit and supplied to a tone coloring circuit so as to produce desired musical sounds. This system is disclosed, for example, in U.S. Pat. No. 3,744,809 issued on July 31, 1973 to Niinomi. According to the synthesizer system, as the keys are depressed, voltage signals hereinafter termed tone pitch signals corresponding to the tone pitches of the operated keys are generated which are used to drive and control voltage controlled type oscillators for producing tone signals corresponding to the tone pitches of the operated keys and a desired musical tone is produced by utilizing these tone signals. This system is disclosed, for example, in U.S. Pat. No. 3,897,709 issued on Aug. 5, 1975 to Hiyoshi et al.
As above described, the electronic musical instruments are constructed to form musical tones by electronic means so that they can produce by a simple manipulation musical tones resembling those of natural musical instruments as well as tones specific to electronical musical instruments and for this reason they have been used extensively. It has been desired strongly to construct electronic musical instruments such that they can also provide the glissando effect and the portamento effect which are used in natural musical instruments thereby improving the effect of performance.
However, if the player wishes to produce the glissando effect in which the musical scale varies stepwisely with a prior art electronic musical instrument described above he must sequentially depress the keys of a keyboard in succession at a constant speed and such performance is especially complicated. Especially when a relatively quick glissando is desired a highly skilled technique is necessary. Where a portamento effect is desired in which the tone pitch is continuously varied from one musical scale note to the other as in one type of a Hawaiian guitar, in the electronic musical instrument of the tone signal keying system described above, it is impossible to obtain the portamento effect, since the frequencies of the tone signals are fixed. For this reason, a special portamento performance device has been added to such electronic musical instruments for obtaining the portamento effect. Such portamento performance device utilizes a variable frequency type oscillator and the oscillation frequency thereof is continuously varied by continuously adjusting a variable resistor or the like for the purpose of producing the portamento effect. This system is disclosed, for example, in U.S. Pat. No. 3,669,422 issued on Oct. 17, 1972 to Yoshihara.
However, the operation of an electronic musical instrument incorporated with a portamento performance device as above described is extremely complicated so that not skilled players can not satisfactorily perform the portamento effect. More particularly, to obtain a portamento effect it is necessary to manually operate the operating element of the portamento performance device while performing a melody as well as an accompaniment on a keyboard unit. Moreover, such operation must satisfy a desired varying speed condition and must stop when the musical tone reaches a destination pitch, and therefore requires excellent skill which will not be attained by not skilled players.